Attributes that can be used for the layered nav are a custom taxonomy, which means you can display them in menus, or display products by attributes. This requires some work on your part, and archives must be enabled.
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function wc_reg_for_menus( $register, $name = '' ) {
if ( $name == 'pa_size' ) $register = true;
return $register;
}
```
Custom attribute slugs are prefixed with `pa_`, so an attribute called `size` would be `pa_size`
Now use your attribute in **Appearance > Menus**. You will notice, however, that it has default blog styling when you click on a link to your taxonomy term.